1.Field of the Invention
The present invention relates to a material conveying apparatus for conveying a material corresponding to rotations of a rotating drum. The present invention also relates to a material processing apparatus for winding a material around the outer circumference of the rotating drum corresponding to the rotations thereof so as to perform an image recording process or an image reading process.
2.Description of the Related Art
An image recording apparatus for tightly winding a material around the outer circumference of a rotating drum and for performing a process such as an image recording process is known.
In the image recording apparatus of this type, the rotating drum is constructed of a metal which is independently rotatable. The rotating drum is in pressing contact with a rubber nipping roller. As the rotating drum is driven, the nipping roller correspondingly rotates. As an example of the material, a photosensitive material (such as a film) is used. When the photosensitive material is supplied between the rotating drum and tile nipping roller, the photosensitive material is nipped and conveyed by the same.
When an image recording process is performed, the photosensitive material is nipped and conveyed by the rotating drum and the nipping roller. During this conveying process, the photosensitive material is wound around the outer circumference of the rotating drum. An image is exposed onto the photosensitive material by a laser diode (LD) or the like. This exposing process is referred to as drum capstan exposure method.
However, with such an image recording apparatus, a very high register tolerance is required. For example, when a photosensitive material whose width is 450 mm and longitudinal size is 600 mm is used, the required register tolerance is 30 .mu.m or less.
Nevertheless, in the conventional image recording apparatus (conveying means) which exposes (records) an image on a photosensitive material being conveyed to it by the above-described rotating drum and the nipping roller, the register tolerance of the image tends to be degraded.
In other words, the deviation of the outer diameter of each portion along the axial line of the above-described rubber nipping roller affects the linear velocity of each circumferential portion along the axial line. Thus, the conveying velocity of the photosensitive material along the axial line by the rotating drum and the nipping roller deviates. In addition, a uniform distribution of the nipping force along the axial line of the nipping roller causes the nipping roller to expand or shrink. Thus, the outer diameter of each portion of the nipping roller varies. Thereby, the rotating circumferential velocity of each portion along the axial line of the nipping roller deviates. The deviation of the linear velocity of each circumferential portion results in a deviation of the conveying velocity along the axial line of the photosensitive material. Moreover, the uniform distribution of the nipping force along the axial line of the nipping roller causes the curvature along the axial line of the photosensitive material at the nipping portion to deviate. The deviation of the curvature results in a deviation of the conveying velocity along the axial line of the photosensitive material.
As the photosensitive material is conveyed, the deviation of the conveying velocity along the axial line of the photosensitive material results in a distortion thereof. Accordingly, a distortion is produced in the exposed image.
In particular, as in a so-called two-up process of an image recording apparatus where separation plates of four colors separated from a color image are disposed in such a way that two are on an upper row of a photosensitive material and the other two are on the lower row thereof, when not only the repeatability of image but a distortion of an exposed image directly affects the register tolerance, the image quality seriously deteriorates.
Moreover, when a color image is recorded on a photosensitive material by a plurality of reciprocative exposing processes, the distortion of the photosensitive material which takes place during the conveying process results in a color distortion or the like. Thus, the quality of the image being exposed is remarkably degraded.